Nowadays, the air pollution problems are becoming increasingly serious in our country and its neighboring regions. In particular, the concentration of fine suspended particles (e.g. Particulate Matter 2.5, PM 2.5) is often too high. Hence, the monitoring of the concentration of suspended particles in the air is getting attention and various detection devices have also been invented accordingly. At present, the particulate matter detecting device on the market for detecting the concentration of suspended particulates works by utilizing a light beam of infrared light or laser light to illuminate the gas in the gas flow channel. When the light beam hits the suspended particles in the gas, scattering occurs. Then, by detecting and collecting the scattered light, the particle size of the suspended particles and the numbers of suspended particles with different sizes in the unit space can be calculated according to the Mie scattering theory.
However, since the particulate matter measuring device has a gas flow path in fluid communication with the external environment and a micro particle sensor for detecting the scattered light is also disposed in the gas flow path, the pollutant from the external environment is easily attached to the micro particle sensor to affect the detection of the scattered light and cause errors in the calculation results. In response to this issue, the current solution is to perform compensation calculation by means of software. In practical, the amount of suspended particles in the air from the external environment tends to vary with time instead of maintaining a fixed value. There is often a certain deviation generated between the compensated and corrected detection value and the actual results. Therefore, when the particulate matter measuring device for detecting the concentration of suspended particles is used, the micro particle sensor is susceptible to the issue of being polluted and shaded by of the suspended particles from the external environment, which is an urgent need for the industry to solve.